1. Field of the Invention
This invention relates generally to bags and methods of making the same and, more particularly, to bags of the leakproof type having an automatic or self opening bottom construction.
2. Description of the Prior Art
Bags of the indicated type are disclosed in U.S. Pat. Nos. 2,496,796, 3,017,069, 3,342,402, 4,490,131, and 4,496,674. As disclosed in these patents, bags of this type generally comprise an outer sheet of paper and an inner liner of an impervious heat sealable material such as a plastic (synthetic resin). The bag is made of a tube and the bottom end of the bag is formed by making a diamond fold comprising a triangular fold portion and a partly rectangular tab fold portion. After the triangular fold portion and tab fold portion are sealed, the bottom of the bag is completed by folding over the tab fold portion onto a previously folded over triangular fold portion. The tab fold portion is caused to adhere to the bottom of the bag by applying suitable adhesive between the contiguous faces of the tab fold portion of the bag bottom structure. During this bottom forming procedure, the bag and the liner are in contiguous overlapping relation so as to form a single bottom structure having a two-ply configuration.
While the prior art bags can be effectively sealed so that the bag can contain many materials without any seepage through the bag bottom, the achievement of a good bottom seal can be attained only by the use of special sealing techniques.